Polyethylene compositions and closures for bottles

ABSTRACT

A dual reactor solution process gives high density polyethylene compositions containing a first ethylene copolymer and a second ethylene copolymer and which have good processability, toughness, and environmental stress crack resistance combined with good organoleptic properties. The polyethylene compositions are suitable for compression molding or injection molding applications and are particularly useful in the manufacture of caps and closures for bottles.

FIELD OF THE INVENTION

The present invention relates to polyethylene compositions that areuseful in the manufacture of molded articles such as closures forbottles.

BACKGROUND OF THE INVENTION

Polymer compositions useful for molding applications, specifically themanufacture of caps and closures for bottles are well known. Screwclosures for example, are typically made from polypropylene (PP) inorder to achieve the necessary cap strength, however, an inner linercomposed of a soft polymer is required to provide necessary sealproperties. The soft inner liner can be made from ethylene/vinyl acetate(EVA), polyvinyl chloride (PVC), butyl rubber or other suitablematerial. The two-part cap is costly, and single part constructions arepreferred to reduce cost.

Accordingly, one-piece closures, such as screw caps have more recentlybeen made from polyethylene resins. The use of high density resin isrequired if the closures are to have sufficient stiffness, while broadermolecular weight distributions are desirable to impart good flowproperties and to improve environmental stress crack resistance (ESCR).

Polyethylene blends produced with conventional Ziegler-Natta or Phillipstype catalysts systems can be made having suitably high density and ESCRproperties, see for example, WO 00/71615 and U.S. Pat. No. 5,981,664.However, the use of conventional catalyst systems typically producessignificant amounts of low molecular weight polymer chains having highcomonomer contents, which results in resins having non-idealorganoleptic properties.

Examples of high density multimodal polyethylene blends made usingconventional catalyst systems for the manufacture of caps or closuresare taught in U.S. Pat. Nos. 2005/0004315A1; 2005/0267249A1; as well asWO 2006/048253, WO 2006/048254, WO 2007/060007; and EP 2,017,302A1.Further high density, multimodal polyethylene blends made by employingconventional Ziegler-Natta catalysts are disclosed in U.S. Pat. Nos.2009/0062463A1; 2009/0198018; 2009/0203848 and in WO 2007/130515, WO2008/136849 and WO 2010/088265.

In contrast to traditional catalysts, the use of so called single sitecatalysts (such as “metallocene” and “constrained geometry” catalysts)provides resin having lower catalyst residues and improved organolepticproperties as taught by U.S. Pat. No. 6,806,338. The disclosed resinsare suitable for use in molded articles. Further resins comprisingmetallocene catalyzed components and which are useful for moldingapplications are described in U.S. Pat. Nos. 7,022,770; 7,307,126;7,396,878 and 7,396,881 and 7,700,708.

U.S. Pat. Appl. No. 2011/0165357A1 discloses a blend of metallocenecatalyzed resins which is suitable for use in pressure resistant pipeapplications.

U.S. Pat. Appl. No. 2006/0241256A1 teaches blends formulated frompolyethylenes made using a hafnocene catalyst in the slurry phase.

A bimodal resin having a relatively narrow molecular weight distributionand long chain branching is described in U.S. Pat. No. 7,868,106. Theresin is made using a bis-indenyl type metallocene catalyst in a dualslurry loop polymerization process and can be used to manufacture capsand closures.

U.S. Pat. No. 6,642,313 discloses multimodal polyethylene resins whichare suitable for use in the manufacture of pipes. A dual reactorsolution process is used to prepare the resins in the presence of aphosphinimine catalyst.

Narrow molecular weight polyethylene blends comprising a metalloceneproduced polyethylene component and a Zielger-Natta or metalloceneproduced polyethylene component are reported in U.S. Pat. No. 7,250,474.The blends can be used in blow molding and injection moldingapplications such as for example, milk bottles and bottle capsrespectively.

In U.S. Pat. Appl. No. 2010/0261848A1 we disclosed a resin compositionhaving a good balance of toughness, ESCR, processability, andorganoleptic properties for use in the manufacture of caps and closures.The resins were made using a single site catalyst system in a dualreactor solution process, to provide bimodal polyethylene compositionsin which comonomer was present in both a high and a low molecular weightcomponent. The disclosed resins had a normal comonomer distribution inthat the low molecular weight component had a larger amount of comonomerthan did the high molecular weight component. We have now found that byadding more comonomer to the high molecular weight component of theseresins, we can improve the ESCR properties. The polyethylenecompositions provided by the present invention also have goodorganoleptic properties, balanced rheological and mechanical propertiesand are suitable for use in the manufacture of closures for bottles.

SUMMARY OF THE INVENTION

The present invention provides a polyethylene composition that can beused in the manufacture of caps and closures for bottles.

The present invention provides a polyethylene composition which has animproved ESCR while maintaining low shear viscosity values at high shearrates which is desirable for high-speed injection or compression moldingapplications.

The present invention provides caps and closures comprising apolyethylene composition made by a two reactor solution phase processand a single site catalyst. Plaques made from the polyethylenecompositions have a good balance of mechanical, processing andorganoleptic properties.

Provided is a closure for bottles, the closure comprising a bimodalpolyethylene composition comprising:

(1) 10 to 70 wt % of a first ethylene copolymer having a melt index, I₂,of less than 0.4 g/10 min; a molecular weight distribution, M_(w)/M_(n),of less than 3.0; and a density of from 0.920 to 0.955 g/cm³; and

(2) 90 to 30 wt % of a second ethylene copolymer having a melt index I₂,of from 100 to 10,000 g/10 min; a molecular weight distribution,M_(w)/M_(n), of less than 3.0; and a density higher than the density ofthe first ethylene copolymer, but less than 0.967 g/cm³;

wherein the density of the second ethylene copolymer is less than 0.037g/cm³ higher than the density of the first ethylene copolymer; the ratioof short chain branching in the first ethylene copolymer (SCB1) to theshort chain branching in the second ethylene copolymer (SCB2) is greaterthan 0.5; and wherein the bimodal polyethylene composition has amolecular weight distribution, M_(W)/M_(n), of from 3 to 11; a densityof at least 0.949 g/cm³; a melt index I₂, of from 0.4 to 5.0 g/10 min;an Mz of less than 400,000; a stress exponent of less than 1.50; and anESCR Condition B (10% IGEPAL) of at least 20 hrs.

Provided is a process to prepare a polyethylene composition, thepolyethylene composition comprising:

(1) 10 to 70 wt % of a first ethylene copolymer having a melt index, I₂,of less than 0.4 g/10 min; a molecular weight distribution, M_(w)/M_(n),of less than 3.0; and a density of from 0.920 to 0.955 g/cm³; and

(2) 90 to 30 wt % of a second ethylene copolymer having a melt index I₂,of from 100 to 10,000 g/10 min; a molecular weight distribution,M_(w)/M_(n), of less than 3.0; and a density higher than the density ofthe first ethylene copolymer, but less than 0.967 g/cm³; wherein thedensity of the second ethylene copolymer is less than 0.037 g/cm³ higherthan the density of the first ethylene copolymer; the ratio of shortchain branching in the first ethylene copolymer (SCB1) to the shortchain branching in the second ethylene copolymer (SCB2) is greater than0.5; and wherein the polyethylene composition has a molecular weightdistribution, M_(W)/M_(n), of from 3 to 11; a density of at least 0.949g/cm³; a melt index I₂, of from 0.4 to 5.0 g/10 min; an Mz of less than400,000; a stress exponent of less than 1.50; and an ESCR Condition B(10% IGEPAL) of at least 20 hrs;

-   -   the process comprising contacting at least one single site        polymerization catalyst system with ethylene and at least one        alpha-olefin comonomer under solution polymerization conditions        in at least two polymerization reactors.

Provided is a bimodal polyethylene composition comprising:

(1) 30 to 60 wt % of a first ethylene copolymer having a melt index, I₂,of less than 0.4 g/10 min; a molecular weight distribution, M_(w)/M_(n),of less than 2.7; and a density of from 0.925 to 0.950 g/cm³; and

(2) 70 to 40 wt % of a second ethylene copolymer having a melt index I₂,of from 100 to 10,000 g/10 min; a molecular weight distribution,M_(w)/M_(n), of less than 2.7; and a density higher than the density ofthe first ethylene copolymer, but less than 0.966 g/cm³;

-   -   wherein the density of the second ethylene copolymer is less        than 0.037 g/cm³ higher than the density of the first ethylene        copolymer; the ratio of short chain branching in the first        ethylene copolymer (SCB1) to the short chain branching in the        second ethylene copolymer (SCB2) is greater than 0.5; and        wherein the bimodal polyethylene composition has a molecular        weight distribution, M_(W)/M_(n), of from 4.0 to 10.0; a density        of from 0.949 to 0.957 g/cm³; a melt index I₂, of from 0.4 to        5.0 g/10 min; a comonomer content of less than 0.75 mol % as        determined by ¹³C NMR; an Mz of less than 400,000; a stress        exponent of less than 1.50; and an ESCR Condition B (10% IGEPAL)        of at least 20 hrs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the relationship between the shear thinning indexSHI_((1,100)) and the melt index, I₂ of polyethylene compositions of thecurrent invention.

DETAILED DESCRIPTION

The present invention is related to caps and closures for bottles and tothe polyethylene compositions used to manufacture them. The polyethylenecompositions are composed of at least two ethylene copolymer components:a first ethylene copolymer and a second ethylene copolymer. Thepolyethylene compositions of the invention have a good balance ofprocessability, toughness, stiffness, environmental stress crackresistance, and organoleptic properties making them ideal materials foruse in manufacturing caps and closures for bottles.

The terms “cap” and “closure” are used interchangeably in the currentinvention, and both connote any suitably shaped molded article forenclosing, sealing, closing or covering etc., a suitably shaped opening,a suitably molded aperture, an open necked structure or the like used incombination with a container, a bottle, a jar and the like.

The terms “homogeneous” or “homogeneously branched polymer” as usedherein define homogeneously branched polyethylene which has a relativelynarrow composition distribution, as indicated by a relatively highcomposition distribution breadth index (CDBI). That is, the comonomer israndomly distributed within a given polymer chain and substantially allof the polymer chains have same ethylene/comonomer ratio.

It is well known that metallocene catalysts and other so called “singlesite catalysts” incorporate comonomer more evenly than traditionalZiegler-Natta catalysts when used for catalytic ethylenecopolymerization with alpha olefins. This fact is often demonstrated bymeasuring the composition distribution breadth index (CDBI) forcorresponding ethylene copolymers. The composition distribution of apolymer can be characterized by the short chain distribution index(SCDI) or composition distribution breadth index (CDBI). The definitionof composition distribution breadth index (CDBI) can be found in PCTpublication WO 93/03093 and U.S. Pat. No. 5,206,075. The CDBI isconveniently determined using techniques which isolate polymer fractionsbased on their solubility (and hence their comonomer content). Forexample, temperature rising elution fractionation (TREF) as described byWild et al. J. Poly. Sci., Poly. Phys. Ed. Vol. 20, p 441, 1982 or inU.S. Pat. No. 4,798,081 can be employed. From the weight fraction versuscomposition distribution curve, the CDBI is determined by establishingthe weight percentage of a copolymer sample that has a comonomer contentwithin 50% of the median comonomer content on each side of the median.Generally, Ziegler-Natta catalysts produce ethylene copolymers with aCDBI of less than about 50%, consistent with a heterogeneously branchedcopolymer. In contrast, metallocenes and other single site catalystswill most often produce ethylene copolymers having a CDBI of greaterthan about 55%, consistent with a homogeneously branched copolymer.

The First Ethylene Copolymer

The first ethylene copolymer of the polyethylene composition of thecurrent invention has a density of from about 0.920 g/cm³ to about 0.955g/cm³; a melt index, I₂, of less than about 0.4 g/10 min; a molecularweight distribution, M_(w)/M_(n), of below about 3.0 and a weightaverage molecular weight, M_(w), that is greater than the M_(w) of thesecond ethylene copolymer. Preferably, the weight average molecularweight, M_(w), of the first ethylene copolymer is at least 110,000.Preferably the first ethylene copolymer is a homogeneously branchedcopolymer.

By the term “ethylene copolymer” it is meant that the copolymercomprises both ethylene and at least one alpha-olefin comonomer.

In an embodiment of the invention, the first ethylene copolymer is madewith a single site catalyst, such as for example a phosphiniminecatalyst.

The comonomer (i.e. alpha-olefin) content in the first ethylenecopolymer can be from about 0.05 to about 3.0 mol %. The comonomercontent of the first ethylene polymer is determined by mathematicaldeconvolution methods applied to a bimodal polyethylene composition (seethe Examples section). The comonomer is one or more suitable alphaolefin such as but not limited to 1-butene, 1-hexene, 1-octene and thelike, with 1-octene being preferred.

The short chain branching in the first ethylene copolymer can be fromabout 0.25 to about 15 short chain branches per thousand carbon atoms(SCB1/1000Cs). In further embodiments of the invention, the short chainbranching in the first ethylene copolymer can be from 0.5 to 15, or from0.5 to 12, or from 0.5 to 10, or from 0.75 to 15, or from 0.75 to 12, orfrom 0.75 to 10, or from 1.0 to 10, or from 1.0 to 8.0, or from 1.0 to5, or from 1.0 to 3 branches per thousand carbon atoms (SCB1/1000Cs).The short chain branching is the branching due to the presence ofalpha-olefin comonomer in the ethylene copolymer and will for examplehave two carbon atoms for a 1-butene comonomer, or four carbon atoms fora 1-hexene comonomer, or six carbon atoms for a 1-octene comonomer, etc.The number of short chain branches in the first ethylene copolymer isdetermined by mathematical deconvolution methods applied to a bimodalpolyethylene composition (see the Examples section). The comonomer isone or more suitable alpha olefin such as but not limited to 1-butene,1-hexene, 1-octene and the like, with 1-octene being preferred.

In an embodiment of the invention, the comonomer content in the firstethylene copolymer is substantially similar or approximately equal (e.g.within about ±0.05 mol %) to the comonomer content of the secondethylene copolymer (as reported for example in mol %).

In an embodiment of the invention, the comonomer content in the firstethylene copolymer is greater than comonomer content of the secondethylene copolymer (as reported for example in mol %).

In an embodiment of the invention, the amount of short chain branchingin the first ethylene copolymer is substantially similar orapproximately equal (e.g. within about ±0.25 SCB/1000Cs) to the amountof short chain branching in the second ethylene copolymer (as reportedin short chain branches, SCB per thousand carbons in the polymerbackbone, 1000Cs).

In an embodiment of the invention, the amount of short chain branchingin the first ethylene copolymer is greater than the amount of shortchain branching in the second ethylene copolymer (as reported in shortchain branches, SCB per thousand carbons in the polymer backbone,1000Cs).

The melt index of the first ethylene copolymer can in an embodiment ofthe invention be above 0.01, but below 0.4 g/10 min.

In an embodiment of the invention, the first ethylene copolymer has aweight average molecular weight M_(w) of from about 110,000 to about250,000. In another embodiment of the invention, the first ethylenecopolymer has a weight average molecular weight M_(w) of greater thanabout 110,000 to less than about 250,000. In further embodiments of theinvention, the first ethylene copolymer has a weight average molecularweight M_(w) of from about 125,000 to about 225,000, or from about135,000 to 200,000.

The density of the first ethylene copolymer is in the present inventionfrom 0.920 to 0.955 g/cm³ or can be a narrower range within this range.For example, in further embodiments of the invention, the density of thefirst ethylene copolymer can be from 0.925 to 0.955 g/cm³, or from 0.925to 0.950 g/cm³, or from 0.925 to 0.945 g/cm³, or from 0.925 to 0.940g/cm³, or from 0.925 to 0.935 g/cm³, or from 0.927 to 0.945 g/cm³, orfrom 0.927 to 0.940 g/cm³, or from 0.927 to 0.935 g/cm³.

In an embodiments of the invention, the first ethylene copolymer has amolecular weight distribution M_(w)/M_(n), of <3.0, or ≦2.7, or <2.7, or≦2.5, or <2.5, or ≦2.3, or from 1.8 to 2.3.

The density and the melt index, I₂, of the first ethylene copolymer canbe estimated from GPC (gel permeation chromatography) and GPC-FTIR (gelpermeation chromatography with Fourier transform infra-red detection)experiments and deconvolutions carried out on the bimodal polyethylenecomposition (see the Examples section).

In an embodiment of the invention, the first ethylene copolymer of thepolyethylene composition is a homogeneously branched ethylene copolymerhaving a weight average molecular weight, M_(W), of at least 110000; amolecular weight distribution, M_(w)/M_(n), of less than 2.7 and adensity of from 0.925 to 0.948 g/cm³.

In an embodiment of the present invention, the first ethylene copolymeris homogeneously branched ethylene copolymer and has a CDBI of greaterthan about 50%, preferably of greater than about 55%. In furtherembodiments of the invention, the first ethylene copolymer has a CDBI ofgreater than about 60%, or greater than about 65%, or greater than about70%.

The first ethylene copolymer can comprise from 10 to 70 weight percent(wt %) of the total weight of the first and second ethylene copolymers.In an embodiment of the invention, the first ethylene copolymercomprises from 20 to 60 weight percent (wt %) of the total weight of thefirst and second ethylene copolymers. In an embodiment of the invention,the first ethylene copolymer comprises from 30 to 60 weight percent (wt%) of the total weight of the first and second ethylene copolymers. Inan embodiment of the invention, the first ethylene copolymer comprisesfrom 40 to 50 weight percent (wt %) of the total weight of the first andsecond ethylene copolymers.

The Second Ethylene Copolymer

The second ethylene copolymer of the polyethylene composition of thecurrent invention has a density below 0.967 g/cm³ but which is higherthan the density of the first ethylene copolymer; a melt index, I₂, offrom about 100 to 10,000 g/10 min; a molecular weight distribution,M_(w)/M_(n), of below about 3.0 and a weight average molecular weightM_(w) that is less than the M_(w) of the first ethylene copolymer.Preferably, the weight average molecular weight, M_(w) of the secondethylene copolymer will be below 45,000. Preferably the second ethylenecopolymer is homogeneously branched copolymer.

By the term “ethylene copolymer” it is meant that the copolymercomprises both ethylene and at least one alpha-olefin comonomer.

In an embodiment of the invention, the second ethylene copolymer is madewith a single site catalyst, such as for example a phosphiniminecatalyst.

The comonomer content in the second ethylene copolymer can be from about0.05 to about 3 mol % as measured by ¹³C NMR, or FTIR or GPC-FTIRmethods. The comonomer content of the second ethylene polymer can alsobe determined by mathematical deconvolution methods applied to a bimodalpolyethylene composition (see the Examples section). The comonomer isone or more suitable alpha olefin such as but not limited to 1-butene,1-hexene, 1-octene and the like, with the use of 1-octene beingpreferred.

The short chain branching in the second ethylene copolymer can be fromabout 0.25 to about 15 short chain branches per thousand carbon atoms(SCB2/1000Cs). In further embodiments of the invention, the short chainbranching in the first ethylene copolymer can be from 0.25 to 12, orfrom 0.25 to 8, or from 0.25 to 5, or from 0.25 to 3, or from 0.25 to 2branches per thousand carbon atoms (SCB2/1000Cs). The short chainbranching is the branching due to the presence of alpha-olefin comonomerin the ethylene copolymer and will for example have two carbon atoms fora 1-butene comonomer, or four carbon atoms for a 1-hexene comonomer, orsix carbon atoms for a 1-octene comonomer, etc. The number of shortchain branches in the second ethylene copolymer can be measured by ¹³CNMR, or FTIR or GPC-FTIR methods. Alternatively, the number of shortchain branches in the second ethylene copolymer can be determined bymathematical deconvolution methods applied to a bimodal polyethylenecomposition (see the Examples section). The comonomer is one or moresuitable alpha olefin such as but not limited to 1-butene, 1-hexene,1-octene and the like, with 1-octene being preferred.

In an embodiment of the invention, the comonomer content in the secondethylene copolymer is substantially similar or approximately equal (e.g.within about ±0.05 mol %) to the comonomer content of the first ethylenecopolymer (as reported for example in mol %).

In an embodiment of the invention, the comonomer content in the secondethylene copolymer is less than the comonomer content of the firstethylene copolymer (as reported for example in mol %).

In an embodiment of the invention, the amount of short chain branchingin the second ethylene copolymer is substantially similar orapproximately equal (e.g. within about ±0.25 SCB/1000C) to the amount ofshort chain branching in the first ethylene copolymer (as reported inshort chain branches, SCB per thousand carbons in the polymer backbone,1000Cs).

In an embodiment of the invention, the amount of short chain branchingin the second ethylene copolymer is less than the amount of short chainbranching in the first ethylene copolymer (as reported in short chainbranches, SCB per thousand carbons in the polymer backbone, 1000Cs).

In the present invention, the density of the second ethylene copolymeris less than 0.967 g/cm³. The density of the second ethylene copolymerin another embodiment of the invention is less than 0.966 g/cm³. Inanother embodiment of the invention, the density of the second ethylenecopolymer is less than 0.965 g/cm³. In another embodiment of theinvention, the density of the second ethylene copolymer is less than0.964 g/cm³. In another embodiment of the invention, the density of thesecond ethylene copolymer is less than 0.963 g/cm³. In anotherembodiment of the invention, the density of the second ethylenecopolymer is less than 0.962 g/cm³.

In an embodiment of the invention, the density of the second ethylenecopolymer is from 0.952 to 0.966 g/cm³ or can be a narrower range withinthis range.

In an embodiment of the invention, the second ethylene copolymer has aweight average molecular weight M_(w) of less than 25,000. In anotherembodiment of the invention, the second ethylene copolymer has a weightaverage molecular weight M_(w) of from about 7,500 to about 23,000. Infurther embodiments of the invention, the second ethylene copolymer hasa weight average molecular weight M_(w) of from about 9,000 to about22,000, or from about 10,000 to about 17,500, or from about 7,500 to17,500.

In an embodiments of the invention, the second ethylene copolymer has amolecular weight distribution of <3.0, or ≦2.7, or <2.7, or ≦2.5, or<2.5, or ≦2.3, or from 1.8 to 2.3.

In an embodiment of the invention, the melt index I₂ of the secondethylene copolymer can be from 20 to 10,000 g/10 min. In anotherembodiment of the invention, the melt index I₂ of the second ethylenecopolymer can be from 100 to 10,000 g/10 min. In yet another embodimentof the invention, the melt index I₂ of the second ethylene copolymer canbe from 1000 to 7000 g/10 min. In yet another embodiment of theinvention, the melt index I₂ of the second ethylene copolymer can befrom 1200 to 10,000 g/10 min. In yet another embodiment of theinvention, the melt index I₂ of the second ethylene copolymer can befrom 1500 to 10,000 g/10 min. In yet another embodiment of theinvention, the melt index I₂ of the second ethylene copolymer can begreater than 1500, but less than 7000 g/10 min.

In an embodiment of the invention, the melt index I₂ of the secondethylene copolymer is greater than 200 g/10 min. In an embodiment of theinvention, the melt index I₂ of the second ethylene copolymer is greaterthan 500 g/10 min. In an embodiment of the invention, the melt index I₂of the second ethylene copolymer is greater than 1000 g/10 min. In anembodiment of the invention, the melt index I₂ of the second ethylenecopolymer is greater than 1200 g/10 min. In an embodiment of theinvention, the melt index I₂ of the second ethylene copolymer is greaterthan 1500 g/10 min.

The density of the second ethylene copolymer may be measured accordingto ASTM D792. The melt index, I₂, of the second ethylene copolymer maybe measured according to ASTM D1238 (when conducted at 190° C., using a2.16 kg weight).

The density and the melt index, I₂, of the second ethylene copolymer canoptionally be estimated from GPC and GPC-FTIR experiments anddeconvolutions carried out on a bimodal polyethylene composition (seethe below Examples section).

In an embodiment of the invention, the second ethylene copolymer of thepolyethylene composition is a homogeneous ethylene copolymer having aweight average molecular weight, M_(W), of at most 45000; a molecularweight distribution, M_(w)/M_(n), of less than 2.7 and a density higherthan the density of said first ethylene copolymer, but less than 0.967g/cm³.

In an embodiment of the present invention, the second ethylene copolymeris homogeneously branched ethylene copolymer and has a CDBI of greaterthan about 50%, preferably of greater than about 55%. In furtherembodiments of the invention, the second ethylene copolymer has a CDBIof greater than about 60%, or greater than about 65%, or greater thanabout 70%.

The second ethylene copolymer can comprise from 90 to 30 wt % of thetotal weight of the first and second ethylene copolymers. In anembodiment of the invention, the second ethylene copolymer comprisesfrom 80 to 40 wt % of the total weight of the first and second ethylenecopolymers. In an embodiment of the invention, the second ethylenecopolymer comprises from 70 to 40 wt % of the total weight of the firstand second ethylene copolymers. In an embodiment of the invention, thesecond ethylene copolymer comprises from 60 to 50 wt % of the totalweight of the first and second ethylene copolymers.

In the present invention, the second ethylene copolymer has a densitywhich is higher than the density of the first ethylene copolymer, butless than about 0.037 g/cm³ higher than the density of the firstethylene copolymer. In an embodiment of the invention, the secondethylene copolymer has a density which is higher than the density of thefirst ethylene copolymer, but less than about 0.035 g/cm³ higher thanthe density of the first ethylene copolymer. In another embodiment ofthe invention, the second ethylene copolymer has a density which ishigher than the density of the first ethylene copolymer, but less thanabout 0.031 g/cm³ higher than the density of the first ethylenecopolymer. In still another embodiment of the invention, the secondethylene copolymer has a density which is higher than the density of thefirst ethylene copolymer, but less than about 0.030 g/cm³ higher thanthe density of the first ethylene copolymer.

In embodiments of the invention, the I₂ of the second ethylene copolymeris at least 100 times, or at least 1000 times, or at least 10,000 the I₂of the first ethylene copolymer.

The Polyethylene Composition

The polyethylene composition of this invention has a broad, bimodal ormultimodal molecular weight distribution. Minimally, the polyethylenecomposition will contain a first ethylene copolymer and a secondethylene copolymer (as defined above) which are of different weightaverage molecular weight (M_(w)).

In the present invention, the polyethylene composition will minimallycomprise a first ethylene copolymer and a second ethylene copolymer (asdefined above) and the ratio (SCB1/SCB2) of the number of short chainbranches per thousand carbon atoms in the first ethylene copolymer (i.e.SCB1) to the number of short chain branches per thousand carbon atoms inthe second ethylene copolymer (i.e. SCB2) will be greater than 0.5 (i.e.SCB1/SCB2>0.5).

In an embodiment of the invention, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) is at least 0.60. Inanother embodiment of the invention, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) is at least 0.75. Inanother embodiment of the invention, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) is at least 1.0. Inyet another embodiment of the invention, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) is at least 1.25. Instill another embodiment of the invention, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) is at least 1.5.

In an embodiment of the invention, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) will be greater than0.5, but less than 1.0.

In an embodiment of the invention, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) will be approximately1.0 (e.g. within ±10%, or from about 0.9 to about 1.1).

In embodiments of the invention, the ratio (SCB1/SCB2) of the shortchain branching in the first ethylene copolymer (SCB1) to the shortchain branching in the second ethylene copolymer (SCB2) will be from0.75 to 12.0, or from 1.0 to 10, or from 1.0 to 7.0, or from 1.0 to 5.0,or from 1.0 to 3.0.

In a specific embodiment of the invention, the polyethylene compositionhas a bimodal molecular weight distribution. In the current invention,the term “bimodal” means that the polyethylene composition comprises atleast two components, one of which has a lower weight average molecularweight and a higher density and another of which has a higher weightaverage molecular weight and a lower density. Typically, a bimodal ormultimodal polyethylene composition can be identified by using gelpermeation chromatography (GPC). Generally, the GPC chromatograph willexhibit two or more component ethylene copolymers, where the number ofcomponent ethylene copolymers corresponds to the number of discerniblepeaks. One or more component ethylene copolymers may also exist as ahump, shoulder or tail relative to the molecular weight distribution ofthe other ethylene copolymer component.

The polyethylene composition of the current invention has a density ofgreater than or equal to 0.949 g/cm³, as measured according to ASTMD792; a melt index, I₂, of from about 0.4 to about 5.0 g/10 min, asmeasured according to ASTM D1238 (when conducted at 190° C., using a2.16 kg weight); a molecular weight distribution, M_(w)/M_(n), of fromabout 3 to about 11, a Z-average molecular weight, M_(z) of less than400,000, a stress exponent of less than 1.50 and an ESCR Condition B at10% of at least 20 hours.

In embodiments of the invention, the polyethylene composition has acomonomer content of less than 0.75 mol %, or less than 0.70 mol %, orless than 0.65 mol %, or less than 0.60 mol %, or less than 0.55 mol %as measured by FTIR or ¹³C NMR methods, with ¹³C NMR being preferred,where the comonomer is one or more suitable alpha olefins such as butnot limited to 1-butene, 1-hexene, 1-octene and the like, with 1-octenebeing preferred. In an embodiment of the invention, the polyethylenecomposition has a comonomer content of from 0.1 to 0.75 mol %, or from0.20 to 0.55 mol %, or from 0.25 to 0.50 mol %.

In the present invention, the polyethylene composition has a density ofat least 0.949 g/cm³. In further embodiments of the invention, thepolyethylene composition has a density of >0.949 g/cm³, or 0.950 g/cm³,or >0.950 g/cm³.

In an embodiment of the current invention, the polyethylene compositionhas a density in the range of from 0.949 to 0.960 g/cm³.

In an embodiment of the current invention, the polyethylene compositionhas a density in the range of from 0.949 to 0.959 g/cm³.

In an embodiment of the current invention, the polyethylene compositionhas a density in the range of from 0.949 to 0.957 g/cm³.

In an embodiment of the current invention, the polyethylene compositionhas a density in the range of from 0.949 to 0.956 g/cm³.

In an embodiment of the current invention, the polyethylene compositionhas a density in the range of from 0.949 to 0.955 g/cm³.

In an embodiment of the current invention, the polyethylene compositionhas a density in the range of from 0.950 to 0.955 g/cm³.

In an embodiment of the current invention, the polyethylene compositionhas a density in the range of from 0.951 to 0.957 g/cm³.

In an embodiment of the current invention, the polyethylene compositionhas a density in the range of from 0.951 to 0.955 g/cm³.

In an embodiment of the invention, the polyethylene composition has amelt index, I₂, of between 0.4 and 5.0 g/10 min according to ASTM D1238(when conducted at 190° C., using a 2.16 kg weight) and includingnarrower ranges within this range. For example, in further embodimentsof the invention, the polyethylene composition has a melt index, I₂, offrom 0.5 to 5.0 g/10 min, or from 0.4 to 3.5 g/10 min, or from 0.4 to3.0 g/10 min, or from 0.5 to 3.5 g/10 min, or from 0.5 to 3.0 g/10 min,or from 1.0 to 3.0 g/10 min, or from about 1.0 to about 2.0 g/10 min, orfrom more than 0.5 to less than 2.0 g10/min.

In an embodiment of the invention, the polyethylene composition has amelt index I₅ of at least 1.0 g/10 min according to ASTM D1238 (whenconducted at 190° C., using a 5 kg weight). In another embodiment of theinvention, the polyethylene composition has a melt index, I₅, of greaterthan about 1.1 g/10 min, as measured according to ASTM D1238 (whenconducted at 190° C., using a 5 kg weight). In further embodiments ofthe invention, the polyethylene composition has a melt index I₅ of atleast 3.0 g/10 min, or at least 4.0 g/10 min. In still furtherembodiments of the invention, the polyethylene composition has a meltindex I₅ of from about 1.0 to about 10.0 g/10 min, or from about 2.0 toabout 8.0 g/10 min, or from about 4.0 to about 7.0 g/10 min, or fromabout 3.0 to about 6.5 g/10 min.

In an embodiment of the invention, the polyethylene composition has ahigh load melt index, I₂₁ of at least 25 g/10 min according to ASTMD1238 (when conducted at 190° C., using a 21 kg weight). In anotherembodiment of the invention, the polyethylene composition has a highload melt index, I₂₁, of greater than about 50 g/10 min. In yet anotherembodiment of the invention, the polyethylene composition has a highload melt index, I₂₁, of greater than about 75 g/10 min. In stillanother embodiment of the invention, the polyethylene composition has ahigh load melt index, I₂₁, of greater than about 100 g/10 min.

In an embodiment of the invention, the ratio of the melt index, I₂, ofthe second ethylene copolymer to the melt index, I₅, of the polyethylenecomposition is from 200 to 1500. In another embodiment of the invention,the ratio of the melt index, I₂, of the second ethylene copolymer to themelt index, I₅, of the polyethylene composition is from 400 to 1300. Inyet another embodiment of the invention, the ratio of the melt index,I₂, of the second ethylene copolymer to the melt index, I₅, of thepolyethylene composition is from 600 to 1200.

In an embodiment of the invention, the polyethylene composition has acomplex viscosity, η* at a shear stress (G*) anywhere between from about1 to about 10 kPa which is between 1,000 to 25,000 Pa·s. In anembodiment of the invention, the polyethylene composition has a complexviscosity, η* at a shear stress (G*) anywhere from about 1 to about 10kPa which is between 1,000 to 10,000 Pa·s.

In an embodiment of the invention, the polyethylene composition has anumber average molecular weight, M_(n), of below about 30,000. Inanother embodiment of the invention, the polyethylene composition has anumber average molecular weight, M_(n), of below about 20,000.

In the present invention, the polyethylene composition has a molecularweight distribution Mw/Mn of from 3 to 11 or a narrower range withinthis range. For example, in further embodiments of the invention, thepolyethylene composition has a M_(w)/M_(n) of from 4.0 to 10.0, or from4.0 to 9.0 or from 5.0 to 10.0, or from 5.0 to 9.0, or from 4.5 to 10.0,or from 4.5 to 9.5, or from 4.5 to 9.0, or from 4.5 to 8.5, or from 5.0to 8.5.

In an embodiments of the invention, the polyethylene composition has aratio of Z-average molecular weight to weight average molecular weight(M_(z)/M_(W)) of from 2.25 to 4.5, or from 2.5 to 4.25, or from 2.75 to4.0, or from 2.75 to 3.75, or between 3.0 and 4.0.

In embodiments of the invention, the polyethylene composition has a meltflow ratio defined as I₂₁/I₂ of >40, or ≧45, or ≧50, or ≧60, or ≧65. Ina further embodiment of the invention, the polyethylene composition hasa melt flow ratio I₂₁/I₂ of from about 40 to about 100, and includingnarrower ranges within this range. For example, the polyethylenecomposition may have a melt flow ratio I₂₁/I₂ of from about 45 to about90, or from about 45 to 80, or from about 45 to 75, or from about 45 to70, or from about 50 to 90, or from about 50 to 80, or from about 50 to75, or from about 50 to 70.

In an embodiment of the invention, the polyethylene composition has amelt flow rate defined as I₂₁/I₅ of less than 25. In another embodimentof the invention, the polyethylene composition has a melt flow ratedefined as I₂₁/I₅ of less than 20.

In an embodiment of the invention, the polyethylene composition has ashear viscosity at about 10⁵ s⁻¹ (240° C.) of less than about 10 (Pa·s).In further embodiments of the invention, the polyethylene compositionhas a shear viscosity at about 10⁵ s⁻¹ (240° C.) of less than 7.5 Pa·s,or less than 6.0 Pa·s.

In an embodiment of the invention, the polyethylene composition has ahexane extractables level of below 0.55 wt %.

In an embodiment of the invention, the polyethylene composition has atleast one type of alpha-olefin that has at least 4 carbon atoms and itscontent is less than 0.75 mol % as determined by ¹³C NMR. In anembodiment of the invention, the polyethylene composition has at leastone type of alpha-olefin that has at least 4 carbon atoms and itscontent is less than 0.65 mol % as determined by ¹³C NMR. In anembodiment of the invention, the polyethylene composition has at leastone type of alpha-olefin that has at least 4 carbon atoms and itscontent is less than 0.55 mol % as determined by ¹³C NMR.

In an embodiment of the invention, the shear viscosity ratio,SVR_((10,1000)) at 240° C. of the polyethylene composition can be fromabout 4.0 to 25, or from 4.0 to 20, or from 4.0 to 17. The shearviscosity ratio SVR_((10,1000)) is determined by taking the ratio ofshear viscosity at shear rate of 10 s⁻¹ and shear viscosity at shearrate of 1000 s⁻¹ as measured with a capillary rheometer at constanttemperature (e.g. 240° C.), and a die with L/D ratio of 20 and diameterof 0.06″.

In an embodiment of the invention, the shear thinning index,SHI_((1,100)) of the polyethylene composition is less than about 10; inanother embodiment the SHI_((1,100)) will be less than about 7. Theshear thinning index (SHI), was calculated using dynamic mechanicalanalysis (DMA) frequency sweep methods as disclosed in PCT applicationsWO 2006/048253 and WO 2006/048254. The SHI value is obtained bycalculating the complex viscosities η* (1) and η* (100) at a constantshear stress of 1 kPa (G*) and 100 kPa (G*), respectively.

In an embodiment of the invention, the SHI_((1,100)) of the polyethylenecomposition satisfies the equation: SHI_((1,100))<−10.58 (log I₂ ofpolyethylene composition in g/10 min)/(g/10 min)+12.94. In anotherembodiment of the invention, the SHI_((1,100)) of the polyethylenecomposition satisfies the equation:

SHI_((1,100))<−5.5(log I ₂ of the polyethylene composition in g/10min)/(g/10 min)+9.66.

In an embodiment of the invention, the polyethylene composition or amolded article made from the polyethylene composition, has anenvironment stress crack resistance ESCR Condition B at 10% of at least20 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C.under condition B).

In an embodiment of the invention, the polyethylene composition or amolded article made from the polyethylene composition, has anenvironment stress crack resistance ESCR Condition B at 10% of at least60 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C.under condition B).

In an embodiment of the invention, the polyethylene composition or amolded article made from the polyethylene composition, has anenvironment stress crack resistance ESCR Condition B at 10% of at least80 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C.under condition B).

In an embodiment of the invention, the polyethylene composition or amolded article made from the polyethylene composition, has anenvironment stress crack resistance ESCR Condition B at 10% of at least120 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C.under condition B).

In an embodiment of the invention, the polyethylene composition or amolded article made from the polyethylene composition, has anenvironment stress crack resistance ESCR Condition B at 10% of at least150 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C.under condition B).

In an embodiment of the invention, the polyethylene composition or amolded article made from the polyethylene composition, has anenvironment stress crack resistance ESCR Condition B at 10% of from 60to 400 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50°C. under condition B).

In an embodiment of the invention, the polyethylene composition or amolded article made from the polyethylene composition, has anenvironment stress crack resistance ESCR Condition B at 10% of from 100to 350 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50°C. under condition B).

In an embodiment of the invention, the polyethylene composition or amolded article made from the polyethylene composition, has anenvironment stress crack resistance ESCR Condition B at 10% of from 60to 250 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50°C. under condition B).

In an embodiment of the invention, the polyethylene composition or amolded article made from the polyethylene composition has a notched Izodimpact strength of at least 60 J/m, as measured according to ASTM D256.

In an embodiment of the invention the polyethylene composition of thecurrent invention has a density of from 0.949 to 0.956 g/cm³; a meltindex, I₂, of from 0.5 to 3.0 g/10 min; a molecular weight distributionof from 4.0 to 10.0; a number average molecular weight, M_(n), of below30,000; a shear viscosity at 10⁵ s⁻¹ (240° C.) of less than 10 (Pa·s), ahexane extractables of less than 0.55%, a notched Izod impact strengthof more than 60 J/m, and an ESCR B at 10% of at least 20 hrs.

In an embodiment of the invention the polyethylene composition of thecurrent invention has a density of from 0.949 to 0.956 g/cm³; a meltindex, I₂, of from 0.5 to 3.0 g/10 min; a molecular weight distributionof from 4.5 to 9.5; a number average molecular weight, M_(n), of below30,000; a shear viscosity at 10⁵ s⁻¹ (240° C.) of less than 7 (Pa·s), ahexane extractables of less than 0.55%, a notched Izod impact strengthof more than 60 J/m and an ESCR B at 10% of at least 80 hrs.

In an embodiment of the invention, the polyethylene composition has astress exponent, defined as Log₁₀[I₆/I₂]/Log₁₀[6.48/2.16], which is1.50. In further embodiments of the invention the polyethylenecomposition has a stress exponent, Log₁₀[I₆/I₂]/Log₁₀[6.48/2.16] of lessthan 1.50, or less than 1.48, or less than 1.45.

In an embodiment of the invention, the polyethylene composition has acomposition distribution breadth index (CDBI), as determined bytemperature elution fractionation (TREF), of ≧60%. In furtherembodiments of the invention, the polyethylene composition will have aCDBI of greater than 65%, or greater than 70%, or greater than 75%, orgreater than 80%.

The polyethylene composition of this invention can be made using anyconventional blending method such as but not limited to physicalblending and in-situ blending by polymerization in multi reactorsystems. For example, it is possible to perform the mixing of the firstethylene copolymer with the second ethylene copolymer by molten mixingof the two preformed polymers. Preferred are processes in which thefirst and second ethylene copolymers are prepared in at least twosequential polymerization stages, however, both in-series or anin-parallel dual reactor process are contemplated for use in the currentinvention. Gas phase, slurry phase or solution phase reactor systems maybe used, with solution phase reactor systems being preferred.

In an embodiment of the current invention, a dual reactor solutionprocess is used as has been described in for example U.S. Pat. No.6,372,864 and U.S. Pat. Appl. No. 20060247373A1 which are incorporatedherein by reference.

Homogeneously branched ethylene copolymers can be prepared using anycatalyst capable of producing homogeneous branching. Generally, thecatalysts will be based on a group 4 metal having at least onecyclopentadienyl ligand that is well known in the art. Examples of suchcatalysts which include metallocenes, constrained geometry catalysts andphosphinimine catalysts are typically used in combination withactivators selected from methylaluminoxanes, boranes or ionic boratesalts and are further described in U.S. Pat. Nos. 3,645,992; 5,324,800;5,064,802; 5,055,438; 6,689,847; 6,114,481 and 6,063,879. Such catalystsmay also be referred to as “single site catalysts” to distinguish themfrom traditional Ziegler-Natta or Phillips catalysts which are also wellknown in the art. In general single site catalysts produce ethylenecopolymers having a molecular weight distribution (M_(W)/M_(n)) of lessthan about 3.0 and a composition distribution breadth index (CDBI) ofgreater than about 50%.

In an embodiment of the current invention, homogeneously branchedethylene polymers are prepared using an organometallic complex of agroup 3, 4 or 5 metal that is further characterized as having aphosphinimine ligand. Such catalysts are known generally asphosphinimine catalysts. Some non-limiting examples of phosphiniminecatalysts can be found in U.S. Pat. Nos. 6,342,463; 6,235,672;6,372,864; 6,984,695; 6,063,879; 6,777,509 and 6,277,931 all of whichare incorporated by reference herein.

Some non-limiting examples of metallocene catalysts can be found in U.S.Pat. Nos. 4,808,561; 4,701,432; 4,937,301; 5,324,800; 5,633,394;4,935,397; 6,002,033 and 6,489,413, which are incorporated herein byreference. Some non-limiting examples of constrained geometry catalystscan be found in U.S. Pat. Nos. 5,057,475; 5,096,867; 5,064,802;5,132,380; 5,703,187 and 6,034,021, all of which are incorporated byreference herein in their entirety.

In an embodiment of the invention, use of a single site catalyst thatdoes not produce long chain branching (LCB) is preferred. Withoutwishing to be bound by any single theory, long chain branching canincrease viscosity at low shear rates, thereby negatively impactingcycle times during the manufacture of caps and closures, such during theprocess of compression molding. Long chain branching may be determinedusing ¹³C NMR methods and may be quantitatively assessed using themethod disclosed by Randall in Rev. Macromol. Chem. Phys. C29 (2 and 3),p. 285.

In an embodiment of the invention, the polyethylene composition willcontain fewer than 0.3 long chain branches per 1000 carbon atoms. Inanother embodiment of the invention, the polyethylene composition willcontain fewer than 0.01 long chain branches per 1000 carbon atoms.

In an embodiment of the invention, the polyethylene composition (definedas above) is prepared by contacting ethylene and at least onealpha-olefin with a polymerization catalyst under solution phasepolymerization conditions in at least two polymerization reactors (foran example of solution phase polymerization conditions see for exampleU.S. Pat. No. 6,372,864; 6,984,695 and U.S. App. No. 20060247373A1 whichare incorporated herein by reference).

In an embodiment of the invention, the polyethylene composition isprepared by contacting at least one single site polymerization catalystsystem (comprising at least one single site catalyst and at least oneactivator) with ethylene and a least one comonomer (e.g. a C3-C8alpha-olefin) under solution polymerization conditions in at least twopolymerization reactors.

In an embodiment of the invention, a group 4 single site catalystsystem, comprising a single site catalyst and an activator, is used in asolution phase dual reactor system to prepare a bimodal polyethylenecomposition by polymerization of ethylene in the presence of analpha-olefin comonomer.

In an embodiment of the invention, a group 4 single site catalystsystem, comprising a single site catalyst and an activator, is used in asolution phase dual reactor system to prepare a bimodal polyethylenecomposition by polymerization of ethylene in the presence of 1-octene.

In an embodiment of the invention, a group 4 phosphinimine catalystsystem, comprising a phosphinimine catalyst and an activator, is used ina solution phase dual reactor system to prepare a bimodal polyethylenecomposition by polymerization of ethylene in the presence of analpha-olefin comonomer.

In an embodiment of the invention, a group 4 phosphinimine catalystsystem, comprising a phosphinimine catalyst and an activator, is used ina solution phase dual reactor system to prepare a bimodal polyethylenecomposition by polymerization of ethylene in the presence of 1-octene.

In an embodiment of the invention, a solution phase dual reactor systemcomprises two solution phase reactors connected in series.

In an embodiment of the invention, a polymerization process to preparethe polyethylene composition comprises contacting at least one singlesite polymerization catalyst system with ethylene and at least onealpha-olefin comonomer under solution polymerization conditions in atleast two polymerization reactors.

In an embodiment of the invention, a polymerization process to preparethe polyethylene composition comprises contacting at least one singlesite polymerization catalyst system with ethylene and at least onealpha-olefin comonomer under solution polymerization conditions in afirst reactor and a second reactor configured in series.

In an embodiment of the invention, a polymerization process to preparethe polyethylene composition comprises contacting at least one singlesite polymerization catalyst system with ethylene and at least onealpha-olefin comonomer under solution polymerization conditions in afirst reactor and a second reactor configured in series, with the atleast one alpha-olefin comonomer being fed exclusively to the firstreactor.

The production of the polyethylene composition of the present inventionwill typically include an extrusion or compounding step. Such steps arewell known in the art.

The polyethylene composition can comprise further polymer components inaddition to the first and second ethylene polymers. Such polymercomponents include polymers made in situ or polymers added to thepolymer composition during an extrusion or compounding step.

Optionally, additives can be added to the polyethylene composition.Additives can be added to the polyethylene composition during anextrusion or compounding step, but other suitable known methods will beapparent to a person skilled in the art. The additives can be added asis or as part of a separate polymer component (i.e. not the first orsecond ethylene polymers described above) added during an extrusion orcompounding step. Suitable additives are known in the art and includebut are not-limited to antioxidants, phosphites and phosphonites,nitrones, antacids, UV light stabilizers, UV absorbers, metaldeactivators, dyes, fillers and reinforcing agents, nano-scale organicor inorganic materials, antistatic agents, lubricating agents such ascalcium stearates, slip additives such as erucimide, and nucleatingagents (including nucleators, pigments or any other chemicals which mayprovide a nucleating effect to the polyethylene composition). Theadditives that can be optionally added are typically added in amount ofup to 20 weight percent (wt %).

One or more nucleating agent(s) may be introduced into the polyethylenecomposition by kneading a mixture of the polymer, usually in powder orpellet form, with the nucleating agent, which may be utilized alone orin the form of a concentrate containing further additives such asstabilizers, pigments, antistatics, UV stabilizers and fillers. Itshould be a material which is wetted or absorbed by the polymer, whichis insoluble in the polymer and of melting point higher than that of thepolymer, and it should be homogeneously dispersible in the polymer meltin as fine a form as possible (1 to 10 μm). Compounds known to have anucleating capacity for polyolefins include salts of aliphatic monobasicor dibasic acids or arylalkyl acids, such as sodium succinate oraluminum phenylacetate; and alkali metal or aluminum salts of aromaticor alicyclic carboxylic acids such as sodium β-naphthoate. Anothercompound known to have nucleating capacity is sodium benzoate. Theeffectiveness of nucleation may be monitored microscopically byobservation of the degree of reduction in size of the spherulites intowhich the crystallites are aggregated.

In an embodiment of the invention, the polymer compositions describedabove are used in the formation of molded articles. For example,articles formed by compression molding and injection molding arecontemplated. Such articles include, for example, caps, screw caps, andclosures for bottles. However, a person skilled in the art will readilyappreciate that the compositions described above may also be used forother applications such as but not limited to film, injection blowmolding, blow molding and sheet extrusion applications.

In an embodiment of the invention, a closure (or cap) is a screw cap fora bottle.

The caps and closures of the current invention can be made according toany known method, including for example injection molding andcompression molding techniques that are well known to persons skilled inthe art. Hence, in an embodiment of the invention a closure (or cap)comprising the polyethylene composition (defined above) is prepared witha process comprising at least one compression molding step and/or atleast one injection molding step.

The caps and closures (including single piece or multi-piece variants)of the invention comprise the polyethylene composition described aboveand have good organoleptic properties, good toughness, as well as goodESCR values. Hence the closures and caps of the current invention arewell suited for sealing bottles containing drinkable water, carbonatedsoft drinks and other foodstuffs, including but not limited to liquidsthat are under an appropriate pressure (i.e. carbonated beverages orappropriately pressurized drinkable liquids).

The invention is further illustrated by the following non-limitingexamples.

EXAMPLES

M_(n), M_(w), and M_(z) (g/mol) were determined by high temperature GelPermeation Chromatography (GPC) with differential refractive index (DRI)detection using universal calibration (e.g. ASTM-D6474-99). GPC data wasobtained using an instrument sold under the trade name “Waters 150c”,with 1,2,4-trichlorobenzene as the mobile phase at 140° C. The sampleswere prepared by dissolving the polymer in this solvent and were runwithout filtration. Molecular weights are expressed as polyethyleneequivalents with a relative standard deviation of 2.9% for the numberaverage molecular weight (“Mn”) and 5.0% for the weight averagemolecular weight (“Mw”). The molecular weight distribution (MWD) is theweight average molecular weight divided by the number average molecularweight, M_(W)/M_(n). The z-average molecular weight distribution isM_(z)/M_(n). Polymer sample solutions (1 to 2 mg/mL) were prepared byheating the polymer in 1,2,4-trichlorobenzene (TCB) and rotating on awheel for 4 hours at 150° C. in an oven. The antioxidant2,6-di-tert-butyl-4-methylphenol (BHT) was added to the mixture in orderto stabilize the polymer against oxidative degradation. The BHTconcentration was 250 ppm. Sample solutions were chromatographed at 140°C. on a PL 220 high-temperature chromatography unit equipped with fourShodex columns (HT803, HT804, HT805 and HT806) using TCB as the mobilephase with a flow rate of 1.0 mL/minute, with a differential refractiveindex (DRI) as the concentration detector. BHT was added to the mobilephase at a concentration of 250 ppm to protect the columns fromoxidative degradation. The sample injection volume was 200 mL. The rawdata were processed with Cirrus GPC software. The columns werecalibrated with narrow distribution polystyrene standards. Thepolystyrene molecular weights were converted to polyethylene molecularweights using the Mark-Houwink equation, as described in the ASTMstandard test method D6474.

Primary melting peak (° C.), heat of fusion (J/g) and crystallinity (%)was determined using differential scanning calorimetry (DSC) as follows:the instrument was first calibrated with indium; after the calibration,a polymer specimen is equilibrated at 0° C. and then the temperature wasincreased to 200° C. at a heating rate of 10° C./min; the melt was thenkept isothermally at 200° C. for five minutes; the melt was then cooledto 0° C. at a cooling rate of 10° C./min and kept at 0° C. for fiveminutes; the specimen was then heated to 200° C. at a heating rate of10° C./min. The DSC Tm, heat of fusion and crystallinity are reportedfrom the 2^(nd) heating cycle.

The short chain branch frequency (SCB per 1000 carbon atoms) ofcopolymer samples was determined by Fourier Transform InfraredSpectroscopy (FTIR) as per the ASTM D6645-01 method. A Thermo-Nicolet750 Magna-IR Spectrophotometer equipped with OMNIC version 7.2a softwarewas used for the measurements.

Comonomer content can also be measured using ¹³C NMR techniques asdiscussed in Randall, Rev. Macromol. Chem. Phys., C29 (2&3), p 285; U.S.Pat. No. 5,292,845 and WO 2005/121239.

Polyethylene composition density (g/cm³) was measured according to ASTMD792.

Hexane extractables were determined according to ASTM D5227.

Shear viscosity was measured by using a Kayeness WinKARS CapillaryRheometer (model #D5052M-115). For the shear viscosity at lower shearrates, a die having a die diameter of 0.06 inch and L/D ratio of 20 andan entrance angle of 180 degrees was used. For the shear viscosity athigher shear rates, a die having a die diameter of 0.012 inch and L/Dratio of 20 was used.

Melt indexes, I₂, I₅, I₆ and I₂₁ for the polyethylene composition weremeasured according to ASTM D1238 (when conducted at 190° C., using a2.16 kg, a 5 kg, a 6.48 kg and a 21 kg weight respectively).

To determine CDBI, a solubility distribution curve is first generatedfor the polyethylene composition. This is accomplished using dataacquired from the TREF technique. This solubility distribution curve isa plot of the weight fraction of the copolymer that is solubilized as afunction of temperature. This is converted to a cumulative distributioncurve of weight fraction versus comonomer content, from which the CDBIis determined by establishing the weight percentage of a copolymersample that has a comonomer content within 50% of the median comonomercontent on each side of the median (See WO 93/03093 and U.S. Pat. No.5,376,439).

The specific temperature rising elution fractionation (TREF) method usedherein was as follows. Polymer samples (50 to 150 mg) were introducedinto the reactor vessel of a crystallization-TREF unit (Polymer ChAR™).The reactor vessel was filled with 20 to 40 ml 1,2,4-trichlorobenzene(TCB), and heated to the desired dissolution temperature (e.g. 150° C.)for 1 to 3 hours. The solution (0.5 to 1.5 ml) was then loaded into theTREF column filled with stainless steel beads. After equilibration at agiven stabilization temperature (e.g. 110° C.) for 30 to 45 minutes, thepolymer solution was allowed to crystallize with a temperature drop fromthe stabilization temperature to 30° C. (0.1 or 0.2° C./minute). Afterequilibrating at 30° C. for 30 minutes, the crystallized sample waseluted with TCB (0.5 or 0.75 mL/minute) with a temperature ramp from 30°C. to the stabilization temperature (0.25 or 1.0° C./minute). The TREFcolumn was cleaned at the end of the run for 30 minutes at thedissolution temperature. The data were processed using Polymer ChARsoftware, Excel spreadsheet and TREF software developed in-house.

The melt index, I₂ and density of the first and second ethylenecopolymers were estimated by GPC and GPC-FTIR deconvolutions asdiscussed further below.

High temperature GPC equipped with an online FTIR detector (GPC-FTIR)was used to measure the comonomer content as the function of molecularweight. Mathematical deconvolutions are performed to determine therelative amount of polymer, molecular weight and comonomer content ofthe component made in each reactor, by assuming that each polymercomponent follows a Flory's molecular weight distribution function andit has a homogeneous comonomer distribution across the whole molecularweight range.

For these single site catalyzed resins, the GPC data from GPCchromatographs was fit based on Flory's molecular weight distributionfunction.

To improve the deconvolution accuracy and consistency, as a constraint,the melt index, I₂, of the targeted resin was set and the followingrelationship was satisfied during the deconvolution:

Log₁₀(I ₂)=22.326528+0.003467*[Log₁₀(M _(n))]³−4.322582*Log₁₀(M_(w))−0.180061*[Log₁₀(M _(z))]²+0.026478*[Log₁₀(M _(z))]³

where the experimentally measured overall melt index, I₂, was used onthe left side of the equation, while M_(n) of each component(M_(w)=2×M_(n) and M_(z)=1.5×M_(w) for each component) was adjusted tochange the calculated overall M_(n), M_(w) and M_(z) of the compositionuntil the fitting criteria were met. During the deconvolution, theoverall M_(n), M_(w) and M_(z) are calculated with the followingrelationships: M_(n)=1/Sum(w_(i)/M_(n)(i)), M_(w)=Sum(w_(i)×M_(w)(i)),M_(z)=Sum(w_(i)×M_(z)(i)²), where i represents the i-th component andw_(i) represents the relative weight fraction of the i-th component inthe composition.

The uniform comonomer distribution (which results from the use of asingle site catalyst) of the resin components (i.e. the first and secondethylene copolymers) allowed the estimation of the short chain branchingcontent (SCB) from the GPC-FTIR data, in branches per 1000 carbon atomsand calculation of comonomer content (in mol %) and density (in g/cm³)for the first and second ethylene copolymers, based on the deconvolutedrelative amounts of first and second ethylene copolymer components inthe polyethylene composition, and their estimated resin molecular weightparameters from the above procedure.

A component (or composition) density model and a component (orcomposition) melt index, I₂, model was used according to the followingequations to calculate the density and melt index I₂ of the first andsecond ethylene polymers:

density=0.979863−0.00594808*(FTIR SCB/1000C)^(0.65)−0.000383133*[Log₁₀(M_(n))]³−0.00000577986*(M _(w) /M _(n))³+0.00557395*(M _(z) /M_(w))^(0.25);

Log₁₀(melt index, I ₂)=22.326528+0.003467*[Log₁₀(M_(n))]³−4.322582*Log₁₀(M _(w))−0.180061*[Log₁₀(M_(z))]²+0.026478*[Log₁₀(M _(z))]³

where the M_(n), M_(w) and M_(z) were the deconvoluted values of theindividual ethylene polymer components, as obtained from the results ofthe above GPC deconvolutions. Hence, these two models were used toestimate the melt indexes and the densities of the components (i.e. thefirst and second ethylene copolymers).

Plaques molded from the polyethylene compositions were tested accordingto the following ASTM methods: Bent Strip Environmental Stress CrackResistance (ESCR) at Condition B at 10% IGEPAL at 50° C., ASTM D1693;notched lzod impact properties, ASTM D256; Flexural Properties, ASTM D790; Tensile properties, ASTM D 638; Vicat softening point, ASTM D 1525;Heat deflection temperature, ASTM D 648.

Dynamic mechanical analyses were carried out with a rheometer, namelyRheometrics Dynamic Spectrometer (RDS-II) or Rheometrics SR5 or ATSStresstech, on compression molded samples under nitrogen atmosphere at190° C., using 25 mm diameter cone and plate geometry. The oscillatoryshear experiments were done within the linear viscoelastic range ofstrain (10% strain) at frequencies from 0.05 to 100 rad/s. The values ofstorage modulus (G′), loss modulus (G″), complex modulus (G*) andcomplex viscosity (η*) were obtained as a function of frequency. Thesame rheological data can also be obtained by using a 25 mm diameterparallel plate geometry at 190° C. under nitrogen atmosphere. TheSHI(1,100) value is calculated according to the methods described in WO2006/048253 and WO 2006/048254.

Examples of the polyethylene compositions were produced in a dualreactor solution polymerization process in which the contents of thefirst reactor flow into the second reactor. This in-series “dualreactor” process produces an “in-situ” polyethylene blend (i.e. thepolyethylene composition). Note, that when an in-series reactorconfiguration is used, un-reacted ethylene monomer, and un-reactedalpha-olefin comonomer present in the first reactor will flow into thedownstream second reactor for further polymerization.

In the present inventive examples, although no co-monomer is feeddirectly to the downstream second reactor, an ethylene copolymer isnevertheless formed in second reactor due to the significant presence ofun-reacted 1-octene flowing from the first reactor to the second reactorwhere it is copolymerized with ethylene. Each reactor is sufficientlyagitated to give conditions in which components are well mixed. Thevolume of the first reactor was 12 liters and the volume of the secondreactor was 22 liters. These are the pilot plant scales. The firstreactor was operated at a pressure of 10500 to 35000 kPa and the secondreactor was operated at a lower pressure to facilitate continuous flowfrom the first reactor to the second. The solvent employed wasmethylpentane. The process operates using continuous feed streams. Thecatalyst employed in the dual reactor solution process experiments was atitanium complex having a phosphinimine ligand, a cyclopentadienideligand and two activatable ligands, such as but not limited to chlorideligands. A boron based co-catalyst was used in approximatelystoichiometric amounts relative to the titanium complex. Commerciallyavailable methylaluminoxane (MAO) was included as a scavenger at anAl:Ti of about 40:1. In addition,2,6-di-tert-butylhydroxy-4-ethylbenzene was added to scavenge freetrimethylaluminum within the MAO in a ratio of Al:OH of about 0.5:1.

The polymerization conditions used to make the inventive compositionsare provided in Table 1.

Inventive and comparative polyethylene composition properties aredescribed in Tables 2.

Calculated properties for the first ethylene copolymer and the secondethylene copolymer for selected comparative and inventive polyethylenecompositions, as obtained from GPC-FTIR deconvolution studies, areprovided in Table 3.

The properties of pressed plaques made from comparative and inventivepolyethylene compositions are provided in Table 4.

Comparative polyethylene compositions (Comparative Examples 1-5) aremade using a single site phosphinimine catalyst in a dual reactorsolution process and have an ESCR at condition B10 of less than 24 hoursand a SCB1/SCB2 ratio of 0.50 or less.

Comparative polyethylene composition (Comparative Example 6), is acommercially available resin from Dow Chemical, DMDA-1250 NT 7, and hasan ESCR at condition B-10 of more than 150 hours and an Mz of greaterthan 400,000.

Inventive polyethylene compositions (Inventive Examples 1-9) are madeusing a single site phosphinimine catalyst in a dual reactor solutionprocess as described above and have an ESCR at condition B10 of greaterthan 20 hours and a SCB1/SCB2 ratio of greater than 0.50. Theseinventive examples also have a Mz values of less than 400,000.

TABLE 1 Reactor Conditions for Inventive Examples Example No. InventiveInventive Inventive Inventive Inventive Example 1 Example 2 Example 3Example 4 Example 5 Reactor 1 Ethylene (kg/h) 35.6 38.1 35.7 36.7 37.5Octene (kg/h) 4.9 4 5.3 4.1 4.8 Hydrogen (g/h) 0.51 0.58 0.51 0.50 0.50Solvent (kg/h) 319.2 329 296.5 296.8 286.8 Reactor Feed Inlet 30 30 3030 30 Temperature (° C.) Reactor Temperature 138.2 140.5 141.1 143.8149.2 (° C.) Titanium Catalyst 0.14 0.10 0.12 0.1 0.1 (ppm) Reactor 2Ethylene (kg/h) 43.6 51.6 43.6 44.9 45.9 Octene (kg/h) 0 0 0 0 0Hydrogen (g/h) 22.2 13.46 22.2 16.4 21 Solvent (kg/h) 106.7 137.2 129.1127.5 135 Reactor Feed Inlet 30 30 30 31.3 29.8 Temperature (° C.)Reactor Temperature 186.9 192.1 186.3 190.9 194 (° C.) Titanium Catalyst0.29 0.23 0.21 0.21 0.24 (ppm) Example No. Inventive Inventive InventiveInventive Example 6 Example 7 Example 8 Example 9 Reactor 1 Ethylene(kg/h) 35.7 35.6 35.7 38.4 Octene (kg/h) 2.6 4.7 4.9 1.5 Hydrogen (g/h)0.45 0.46 0.46 0.62 Solvent (kg/h) 256.6 259.1 258.9 346.3 Reactor FeedInlet 30 30 30 30 Temperature (° C.) Reactor Temperature 152.5 151 147141.1 (° C.) Titanium Catalyst 0.08 0.13 0.10 0.10 (ppm) Reactor 2Ethylene (kg/h) 43.6 43.6 43.6 51.9 Octene (kg/h) 0 0 0 0 Hydrogen (g/h)10.2 21.59 16.21 15.07 Solvent (kg/h) 171.6 167 167.1 121.7 Reactor FeedInlet 30 30 30 30 Temperature (° C.) Reactor Temperature 185.7 186.2186.4 192.8 (° C.) Titanium Catalyst 0.13 0.22 0.20 0.31 (ppm)

TABLE 2 Resin Properties Example No. Comparative Comparative ComparativeComparative Comparative Example 1 Example 2 Example 3 Example 4 Example5 Density (g/cm³) 0.9534 0.9523 0.9526 0.952 0.953 Rheology/FlowProperties Melt Index I₂ (g/10 min) 1.88 0.625 1.42 1.92 0.68 Melt FlowRatio (I₂₁/I₂) 56.9 51.2 50.5 77.1 73.2 Stress Exponent 1.41 1.38 1.361.38 1.38 I₂₁ (g/10 min) 107 33.1 71.3 146.0 49.8 I₅ (g/10 min) 4.23I₂₁/I₅ 16.86 Shear Viscosity at 10⁵ 5.8 s⁻¹ (240° C., Pa-s) ShearViscosity Ratio 12.0 η(10 s⁻¹)/η(1000 s⁻¹) at 240° C. DMA Data (190° C.)η* = 5832 Pa*s at G* = 2.099 kPa; η* = 5591 Pa*s at G* = 2.795 kPa GPCM_(n) 14393 22392 17827 9891 12424 M_(w) 91663 109626 105289 77319104353 M_(z) 325841 299470 282159 245479 327007 Polydispersity Index6.37 4.9 5.91 7.82 8.4 (M_(w)/M_(n)) M_(z)/M_(w) 3.55 3.56 2.68 3.173.13 Branch Frequency - FTIR (uncorrected for chain end —CH₃)Uncorrected 2.2 2 2.2 3.7 2.5 SCB/1000C Uncorrected 0.4 0.4 0.4 0.7 0.5comonomer content (mol %) Comonomer ID Octene octene octene octeneoctene Comonomer mol % measured by ¹³C-NMR Hexyl+ branches(≧4 0.3 0.20.28 carbon atoms), mol % Slow-CTREF CDBI₅₀ (%) 63 DSC Primary MeltingPeak 128.3 129.7 129.11 126.8 128.42 (° C.) Heat of Fusion (J/g) 204.7198.2 207.7 200.3 213.80 Crystallinity (%) 70.58 68.34 71.61 69.08 73.72Other properties Hexane Extractables 0.44 0.46 0.32 0.73 0.57 (wt %)VICAT Soft. Pt. (° C.) - 126 127 127.3 122 125 Plaque Heat DeflectionTemp. 72 71 68.2 68 71 [C.] @ 66 PSI Example No. Comparative InventiveInventive Inventive Inventive Example 6 Example 1 Example 2 Example 3Example 4 Density (g/cm³) 0.955 0.9529 0.9524 0.9524 0.9523Rheology/Flow Properties Melt Index I₂ (g/10 min) 1.5 1.57 2.94 1.69 1.5Melt Flow Ratio (I₂₁/I₂) 66 58 44.1 61 54.8 Stress Exponent 1.58 1.381.36 1.38 1.4 I₂₁ (g/10 min) 99 90 129 104 82.3 I₅ (g/10 min) 5.31 4.724.94 4.5 I₂₁/I₅ 18.64 19.07 21.05 18.29 Shear Viscosity at 10⁵ 6.2 5.16.2 4.8 5.8 s⁻¹ (240° C., Pa-s) Shear Viscosity Ratio 11.3 13.5 8.1 13.014.8 η(10 s⁻¹)/η(1000 s⁻¹) at 240° C. DMA Data (190° C.) η* = 5294 η* =4889 Pa*s at G* = Pa*s at G* = 2.647 kPa; 2.445 kPa; η* = 5106 η* = 4739Pa*s at G* = Pa*s at G* = 3.547 kPa 3.292 kPa GPC M_(n) 10240 1052415679 10579 13309 M_(w) 106992 83712 74090 86319 88295 M_(z) 533971256210 215369 291056 278141 Polydispersity Index 10.45 7.95 4.73 8.166.63 (M_(w)/M_(n)) M_(z)/M_(w) 4.99 3.06 2.91 3.37 3.15 BranchFrequency - FTIR (uncorrected for chain end —CH₃) Uncorrected 2.3 3 1.83 2.1 SCB/1000C Uncorrected 0.5 0.6 0.4 0.6 0.4 comonomer content (mol%) Comonomer ID hexene octene octene octene octene Comonomer mol %measured by ¹³C-NMR Hexyl+ branches(≧4 0.4 0.4 0.3 carbon atoms), mol %Slow-CTREF CDBI₅₀(%) 63.4 81.8 86.2 80.4 76.5 DSC Primary Melting Peak130.06 127.3 128.8 127.5 129 (° C.) Heat of Fusion (J/g) 217.4 203.8206.1 207.3 209 Crystallinity (%) 74.98 70.27 71.08 71.48 72.08 Otherproperties Hexane Extractables 0.36 0.36 0.22 0.42 0.25 (wt %) VICATSoft. Pt. (° C.) - 126.8 125.2 126.8 124.8 126.4 Plaque Heat DeflectionTemp. 73 68 74.1 76 67.3 [C.] @ 66 PSI Example No. Inventive InventiveInventive Inventive Inventive Example 5 Example 6 Example 7 Example 8Example 9 Density (g/cm³) 0.9532 0.9527 0.9534 0.9522 0.9568Rheology/Flow Properties Melt Index I₂ (g/10 min) 1.78 1.29 2.05 1.311.68 Melt Flow Ratio (I₂₁/I₂) 55.6 44.1 55 64 54.2 Stress Exponent 1.371.35 1.34 1.39 1.40 I₂₁ (g/10 min) 99.1 57 113 83 91 I₅ (g/10 min) 5.336.21 I₂₁/I₅ 18.59 18.20 Shear Viscosity at 10⁵ 5.1 6.3 5.0 5.8 6.0 s⁻¹(240° C., Pa-s) Shear Viscosity Ratio 13.3 11.6 12.1 14.8 11.2 η(10s⁻¹)/η(1000 s⁻¹) at 240° C. DMA Data (190° C.) η* = 6707 η* = 6688 Pa*sat G* = Pa*s at G* = 2.413 kPa; 2.407 kPa; η* = 6465 η* = 6472 Pa*s atG* = Pa*s at G* = 3.232 kPa 3.236 kPa GPC M_(n) 9716 18449 11145 1402115110 M_(w) 84943 93080 80630 93175 85227 M_(z) 288665 272788 243944303823 287035 Polydispersity Index 8.74 5.05 7.23 6.65 5.64(M_(w)/M_(n)) M_(z)/M_(w) 3.40 2.93 3.03 3.26 3.37 Branch Frequency -FTIR (uncorrected for chain end —CH₃) Uncorrected 2.5 1.7 2.8 2.2 1.3SCB/1000C Uncorrected 0.5 0.3 0.6 0.4 0.3 comonomer content (mol %)Comonomer ID Octene octene octene octene octene Comonomer mol % measuredby ¹³C-NMR Hexyl+ branches(>=4 carbon atoms), mol % Slow-CTREF CDBI₅₀(%)75.2 86.2 79.7 80.4 77.8 DSC Primary Melting Peak 128.3 129.8 127.9128.4 130.7 (° C.) Heat of Fusion (J/g) 207.3 208.5 211.1 205.4 213.8Crystallinity (%) 71.48 71.9 72.8 70.82 73.73 Other properties HexaneExtractables 0.33 0.25 0.38 0.27 0.24 (wt %) VICAT Soft. Pt. (° C.) -125.4 128.2 125.2 126.2 128.4 Plaque Heat Deflection Temp. 69.8 68.266.8 69 77.6 [C.] @ 66 PSI

TABLE 3 Polyethylene Component Properties Example No. ComparativeComparative Comparative Comparative Comparative Inventive InventiveInventive Inventive Example 1 Example 2 Example 3 Example 4 Example 5Example 3 Example 4 Example 5 Example 7 Density (g/cm³) 0.9534 0.95230.9526 0.952 0.953 0.9524 0.9523 0.9532 0.9534 I₂ (g/10 min.) 1.88 0.6251.42 1.92 0.68 1.69 1.5 1.78 2.05 Stress Exponent 1.41 1.38 1.36 1.381.38 1.38 1.4 1.37 1.34 MFR (I₂₁/I₂) 56.9 51.2 50.5 77.1 73.2 61 54.855.6 55 Mw/Mn 6.37 4.9 6.34 7.82 8.39 8.16 6.63 8.74 7.23 1^(st)Ethylene Copolymer weight % 0.43 0.43 0.433 0.426 0.449 0.455 0.4540.454 0.453 Mw 162400 214300 176200 169500 213200 165100 168100 162700157200 I₂ (g/10 min.) 0.13 0.05 0.10 0.11 0.05 0.13 0.12 0.13 0.15Density 1, 0.9389 0.9356 0.9334 0.9382 0.9363 0.9325 0.9302 0.93220.9316 d1 (g/cm³) SCB1 per 1000Cs 0.15 0.13 1.07 0.18 0.06 1.57 2.241.71 2.02 mol % octene 0.03 0.03 0.21 0.04 0.01 0.31 0.45 0.34 0.402^(nd) Ethylene Copolymer weight % 0.57 0.57 0.567 0.574 0.551 0.5450.546 0.546 0.547 Mw 18500 25600 17300 11700 14300 11100 14900 1210011400 I₂ (g/10 min.) 736 190 979 5082 2148 6318 1817 4419 5739 Density2, 0.9559 0.9522 0.9528 0.9559 0.9565 0.9614 0.9555 0.959 0.9577 d2(g/cm³) SCB2 per 1000Cs 1.06 1.37 2.16 2.1 1.42 0.63 1.64 1.08 1.59 mol% octene 0.21 0.27 0.43 0.42 0.28 0.13 0.33 0.22 0.32 Estimated 0.0170.0166 0.0194 0.0177 0.0202 0.0289 0.0253 0.0268 0.0261 (d2 − d1), g/cm³Estimated 0.91 1.24 1.09 1.92 1.36 −0.94 −0.6 −0.63 −0.43 (SCB2 − SCB1)SCB1/SCB2 0.14 0.09 0.50 0.09 0.04 2.5 1.37 1.58 1.27

TABLE 4 Plaque Properties Example No. Comparative ComparativeComparative Comparative Comparative Example 1 Example 2 Example 3Example 4 Example 5 Environmental Stress Crack Resistance ESCR Cond. Bat 10% (hrs) <24 <24 <24 <24 <24 Flexural Properties (Plaques) FlexSecant Mod. 1% (MPa) 1035 1070 1198 1062 1201 Flex Sec Mod 1% (MPa) 2537 38 34 41 Dev. Flex Secant Mod. 2% (MPa) 877 906 1011 904 1002 FlexSec Mod 2% (MPa) 19 29 22 28 32 Dev. Flexural Strength (MPa) 31.5 33.435.1 33 35.5 Flexural Strength Dev. 0.6 0.7 0.4 0.9 0.6 (MPa) TensileProperties (Plaques) Elong. at Yield (%) 10.2 10.3 10 10.3 10.2 Elong.at Yield Dev. (%) 0.8 1 0 0.3 0.4 Yield Strength (MPa) 26.6 25.4 26.325.7 26.9 Yield Strength Dev. (MPa) 0.3 0.4 0.6 0.6 0.3 Ultimate Elong.(%) 920 1003 858 535 800 Ultimate Elong. Dev. (%) 94.6 23.7 37 167.486.1 Ultimate Strength (MPa) 21.5 33.8 21.4 14.8 20.7 Ultimate StrengthDev. 4.1 1.1 1.8 0.7 6.7 (MPa) Sec Mod 1% (MPa) 1374 1138 1294 1244 1237Sec Mod 1% (MPa) Dev. 276.4 210.8 188 47.1 83 Sec Mod 2% (MPa) 937 834900 858 888 Sec Mod 2% (MPa) Dev. 71 61 44 24 47 Impact Properties(Plaques) Notched Izod Impact (J/m) 76 139 64.1 69.4 97.1 IZOD DV (J/m)7 7 5.3 6.9 2.8 Example No. Comparative Inventive Inventive InventiveInventive Example 6 Example 1 Example 2 Example 3 Example 4Environmental Stress Crack Resistance ESCR Cond. B at 10% (hrs) 196 30923 212 86 Flexural Properties (Plaques) Flex Secant Mod. 1% (MPa) 13721274 1247 1267 1295 Flex Sec Mod 1% (MPa) 87 39 44 19 23 Dev. FlexSecant Mod. 2% (MPa) 1167 1064 1035 1060 1085 Flex Sec Mod 2% (MPa) 4529 33 14 21 Dev. Flexural Strength (MPa) 40.4 37.5 36.7 37.1 37.3Flexural Strength Dev. 1 0.8 0.4 0.3 0.4 (MPa) Tensile Properties(Plaques) Elong. at Yield (%) 9 9 10 8 10 Elong. at Yield Dev. (%) 1 1 10 0 Yield Strength (MPa) 28.5 26 25.6 26.4 26.3 Yield Strength Dev.(MPa) 0.3 0.2 0.1 0.3 0.3 Ultimate Elong. (%) 870 701 988 762 891Ultimate Elong. Dev. (%) 69 106 58 98 23 Ultimate Strength (MPa) 26.821.8 32.2 24.7 33.3 Ultimate Strength Dev. 5.5 6.8 1.9 7.4 2 (MPa) SecMod 1% (MPa) 1696 1483 1256 1331 1230 Sec Mod 1% (MPa) Dev. 279 121 333241 90 Sec Mod 2% (MPa) 1118 973 880 939 913 Sec Mod 2% (MPa) Dev. 90 3388 62 34 Impact Properties (Plaques) Notched Izod Impact (J/m) 80.1 74.769.4 69.4 80.1 IZOD DV (J/m) 5.3 0.0 0.0 0.0 2.7 Example No. InventiveInventive Inventive Inventive Inventive Example 5 Example 6 Example 7Example 8 Example 9 Environmental Stress Crack Resistance ESCR Cond. Bat 10% (hrs) 83 60 73 157 24 Flexural Properties (Plaques) Flex SecantMod. 1% (MPa) 1304 1240 1318 1260 1402 Flex Sec Mod 1% (MPa) 57 31 37 2548 Dev. Flex Secant Mod. 2% (MPa) 1092 1026 1098 1049 1159 Flex Sec Mod2% (MPa) 40 26 24 15 35 Dev. Flexural Strength (MPa) 37.6 36.1 38.2 36.939.8 Flexural Strength Dev. 0.8 0.6 0.3 0.6 1.1 (MPa) Tensile Properties(Plaques) Elong. at Yield (%) 9 10 8 9 10 Elong. at Yield Dev. (%) 0 0 01 0 Yield Strength (MPa) 26.4 25.6 26.9 26.1 28.2 Yield Strength Dev.(MPa) 0.2 0.2 0.2 0.2 0.6 Ultimate Elong. (%) 862 974 766 836 923Ultimate Elong. Dev. (%) 47 35 130 103 104 Ultimate Strength (MPa) 29.736.3 22.9 29.6 26.9 Ultimate Strength Dev. 2.7 1.5 7 5.5 6.9 (MPa) SecMod 1% (MPa) 1197 1333 1429 1395 1367 Sec Mod 1% (MPa) Dev. 128 213 183217 190 Sec Mod 2% (MPa) 881 893 979 934 966 Sec Mod 2% (MPa) Dev. 40 7052 73 67 Impact Properties (Plaques) Notched Izod Impact (J/m) 64.1128.1 64.1 80.1 90.7 IZOD DV (J/m) 2.1 5.3 0.0 0.0 5.3

As can be seen from the data provided in Tables 2, 3 and 4, theInventive polyethylene compositions (Inventive Examples 1-9) which havea ratio of short chain branching SCB1/SCB2 of greater than 0.5, haveimproved ESCR B properties while maintaining good processability.

Shear Thinning Index

As shown in FIG. 1, the inventive polyethylene compositions 1, 3, 5, 6and 8 do not satisfy the equation SHI_((1,100))≧−10.58 (log I₂ of thepolyethylene composition in g/10 min)/(g/10 min)+12.94, which is aproperty of the blends taught in WO 2006/048253. As shown in FIG. 1, theinventive polyethylene compositions 1, 3, 5, 6 and 8 do not satisfy theequation:

SHI_((1,100))≧−5.5(log I₂ of the polyethylene composition in g/10min)/(g/10 min)+9.66, which is a property of the blends taught in and WO2006/048254.

1. A bimodal polyethylene composition comprising: (1) 10 to 70 wt % of a first ethylene copolymer having a melt index I₂, of less than 0.4 g/10 min; a molecular weight distribution M_(w)/M_(n), of less than 3.0; and a density of from 0.920 to 0.955 g/cm³; and (2) 90 to 30 wt % of a second ethylene copolymer having a melt index I₂, of from 100 to 10,000 g/10 min; a molecular weight distribution M_(w)/M_(n), of less than 3.0; and a density higher than the density of said first ethylene copolymer, but less than 0.967 g/cm³; wherein the density of said second ethylene copolymer is less than 0.037 g/cm³ higher than the density of said first ethylene copolymer; the ratio (SCB1/SCB2) of the number of short chain branches per thousand carbon atoms in said first ethylene copolymer (SCB1) to the number of short chain branches per thousand carbon atoms in said second ethylene copolymer (SCB2) is greater than 0.5; and wherein said bimodal polyethylene composition has a molecular weight distribution M_(w)/M_(n), of from 3 to 11; a density of at least 0.949 g/cm³; a melt index I₂, of from 0.4 to 5.0 g/10 min; an M_(z) of less than 400,000; a stress exponent of less than 1.50; and an ESCR Condition B (10% IGEPAL) of at least 20 hrs.
 2. The bimodal polyethylene composition of claim 1 wherein the ratio (SCB1/SCB2) of the number of short chain branches per thousand carbon atoms in said first ethylene copolymer (SCB1) to the number of short chain branches per thousand carbon atoms in said second ethylene copolymer (SCB2) is at least 1.0.
 3. The bimodal polyethylene composition of claim 1 wherein the ratio (SCB1/SCB2) of the number of short chain branches per thousand carbon atoms in said first ethylene copolymer (SCB1) to the number of short chain branches per thousand carbon atoms in said second ethylene copolymer (SCB2) is at least 1.5.
 4. The bimodal polyethylene composition of claim 1 wherein said bimodal polyethylene composition has an ESCR Condition B (10% IGEPAL) of at least 60 hrs.
 5. The bimodal polyethylene composition of claim 1 wherein said bimodal polyethylene composition has an ESCR Condition B (10% IGEPAL) of at least 120 hrs.
 6. The bimodal polyethylene composition of claim 1 wherein said bimodal polyethylene composition has a molecular weight distribution, M_(w)/M_(n), of from 4.5 to 10.0.
 7. The bimodal polyethylene composition of claim 1 wherein said bimodal polyethylene composition has melt index I₂, of from 0.4 to 3.0 g/10 min.
 8. The bimodal polyethylene composition of claim 1 wherein said first ethylene copolymer has a density of from 0.925 to 0.950 g/cm³.
 9. The bimodal polyethylene composition of claim 1 wherein said second ethylene copolymer has a density of less than 0.965 g/cm³.
 10. The bimodal polyethylene composition of claim 1 wherein said bimodal polyethylene composition has a density of from 0.951 to 0.957 g/cm³.
 11. The bimodal polyethylene composition of claim 1 wherein the density of said second ethylene copolymer is less than 0.035 g/cm³ higher than the density of said first ethylene copolymer.
 12. The bimodal polyethylene composition of claim 1 wherein said second ethylene copolymer has a melt index I₂, of greater than 1500 g/10 min.
 13. The bimodal polyethylene composition of claim 1 wherein said first and second ethylene copolymers have a M_(w)/M_(n) of less than 2.5.
 14. The bimodal polyethylene composition of claim 1 wherein said bimodal polyethylene composition has a composition distribution breadth index (CDBI) of greater than 65%.
 15. The bimodal polyethylene composition of claim 1 wherein said bimodal polyethylene composition comprises: from 30 to 60 wt % of said first ethylene copolymer; and from 70 to 40 wt % of said second ethylene copolymer.
 16. The bimodal polyethylene composition of claim 1 wherein said bimodal polyethylene composition has a comonomer content of less than 0.75 mol % as determined by ¹³C NMR.
 17. The bimodal polyethylene composition of claim 1 wherein the bimodal polyethylene composition further comprises one or more nucleating agents.
 18. The bimodal polyethylene composition of claim 1 wherein said first and second ethylene copolymers are copolymers of ethylene and 1-octene. 19-20. (canceled)
 21. The bimodal polyethylene composition of claim 1 wherein said bimodal polyethylene composition is prepared by contacting ethylene and an alpha-olefin with a polymerization catalyst under solution polymerization conditions in a least two polymerization reactors. 22-30. (canceled)
 31. The bimodal polyethylene composition of claim 1 wherein the density of said second ethylene copolymer is less than 0.031 g/cm³ higher than the density of said first ethylene copolymer. 31-33. (canceled) 